This invention relates generally to transducer arrays for use in multi-jet, drop-on-demand ink jet printers, the printers which employ such transducer arrays and methods of making and using the same.
In liquid droplet ejecting systems of the drop-on-demand type, also known as impulse ink jet printers, a piezoceramic transducer is used to expel ink as droplets from a small nozzle or jet. An array of such jets is often utilized in high-speed, high-resolution printers where, as is well-known, for a fixed angle of the printer head, the printing rate and printed image resolution is dependent upon the number of jets, spacing therebetween and the droplet emission frequency.
Examples of suitable ink jet printers are described in U.S. Pat. No. 4,459,601, issued Jul. 10, 1984 to Stuart D. Howkins, U.S. Pat. No. 4,714,934 to Rogers, issued Dec. 22, 1987, U.S. Pat. No. 4,768,266 to De Young, issued Sep. 6, 1988, and U.S. Pat. No. 4,751,774 to De Young, et al., issued Jun. 21, 1988, each assigned to the assignee of the present invention and incorporated herein by reference. In those arrangements, an ink jet apparatus of the demand or impulse type comprises a chamber and an orifice from which droplets of ink are ejected in response to the state of energization of a transducer, wherein each transducer is formed of a single elongated strip or rod of piezoceramic material. The transducer communicates with the chamber through a foot forming a movable wall. The transducer expands and contracts in a direction having at least one component extending parallel with the direction of droplet ejection through the orifice, and is expanded in such direction in response to an electric field. The electric field results from an energizing voltage applied transverse to the axis of elongation. The amount of voltage required for a given transducer displacement (expansion or contraction) is dependant on the length of the elongated strip of piezoceramic material. However, longer strips tend to have lower resonant frequencies, which limits the maximum obtainable drop rate or frequency. In addition, lower resonant frequencies are more difficult to dampen.
One problem common to high-speed, high resolution, drop-on-demand ink jet printers occurs because the jets of an array are spaced very close to one another. That is, the response of one jet in an array to its drive voltage can be affected by the simultaneous application of a drive voltage to another nearby jet. This can result in a phenomenon, known in the art as "mechanical cross-talk", where pressure waves are transmitted through the solid material in which the jets are formed, or another phenomenon, known in the art as "electrical cross-talk", where relatively large drive voltages necessary for substantial displacement of transducers utilized in the prior art cause the subsequent pulsing of an inappropriate jet. This is primarily caused by the electrical impedance of the transducer, which tends to be relatively high in transducer designs employing a single elongated strip or rod of piezoceramic material.
One approach to address the problem of mechanical cross-talk is discussed in U.S. Pat. No. 4,439,780, issued Mar. 27, 1984 to De Young, et al. and assigned to the assignee of the present invention and incorporated herein by reference. In that arrangement, an ink jet array comprises a plurality of elongated rod transducers coupled to a plurality of ink jet chambers through a diaphragm. The transducers are supported only at their longitudinal extremities. The support at the extremity remote from the chamber is provided such that no longitudinal motion along the axis of elongation of the transducers occurs, while the support at the other extremity includes bearings which substantially preclude lateral movement of the transducers transverse to their axis of elongation but permit the longitudinal movement thereof along the axis, thus minimizing mechanical cross-talk between jets within the array.
Other characteristic problems which are encountered in the implementation of high-speed, high-resolution impulse ink jet printers do not impact so much upon their operation, but indeed impact upon their fabrications. For example, the relatively small sizes of transducer elements used in densely packed arrays make them difficult to handle.
One approach towards the resolution of the above-described problems is described in U.S. Pat. No. 5,128,694 to Kanayama. As discussed therein, a head for an ink-jet printer includes a piezoelectric transducer formed of a laminated structure in which a plurality of layers of piezoelectric material and a plurality of layers of electrodes are stacked and laminated together in the shape of a rectangular block. Parallel slits extend through four of the nine stacked layers of piezoelectric material, forming two "pressure portions" provided in communication with two ink-jet chambers 18a and 18b through a plate 12. The two "pressure portions" are connected together by a stack of five layers of piezoelectric material. European Patent Application Publication No. 402,172 to Kubota describes a similar arrangement. Since each of these transducer arrangements employ a layer or several layers of piezoelectric material to interconnect plural layered fingers, it is believed that a significant amount of mechanical cross-talk will occur between the plural layered fingers through the interconnecting piezoelectric layer.